1. Field of the Invention
The present invention relates generally to hydroforming, and specifically to hydroforming using a self-aligning and activating die system.
2. Discussion of the Prior Art
Various processes exist to create complex shapes and cross sections. One such process is hydroforming. Hydroforming is a process used to form metal by applying pressurized fluid to the interior wall of a tube (or a sheet of material). Hydroforming creates complex components from inexpensive tubing or sheeting and eliminates the need for expensive multi-piece stamped and welded assemblies.
Tube hydroforming generally involves placing a straight or pre-formed tube in a die set. Pre-formed tubes are created by manually operated benders or computer numeric controlled (CNC) benders. The creation of pre-formed tubes by CNC benders is well known in the prior art. The die set used in tube hydroforming is contained within a large forming press. In hydroforming, the tube is placed in the die set, the die set is closed and pressurized fluid is introduced into the ends of the tube. Fluid pressure forces the walls of the tube to expand and conform to the shape of the die cavity. The size of the press depends on the surface area, wall thickness and/or the geometry of the required pieces.
Currently, large presses are required to create the force necessary to keep the die halves or molds from separating during hydroforming. A typical high tonnage (greater than 500 ton) vertical hydroform press requires special installation and needs deep foundations of reinforced concrete. These presses can weigh many tons and can be over twenty (20) feet in height.
Vertical hydroform presses are also expensive. Their large size and weight usually require these presses to be assembled in one facility, disassembled, shipped in sections, and re-assembled on-site. This also increases cost and star-up time. Thus, conventional vertical hydroform presses are long-term investments.
Conventional hydroform dies/molds are similarly expensive. The dies/molds are typically machined from at least two rectangular solid steel billets. Often, billet machining will remove as much as fifty percent of the original material, thus adding to overall cost. Nevertheless, the dies must be strong enough to maintain the die set in a closed position during hydroforming.
Due to the size and expense of hydroform systems, hydroforming part production is usually restricted to high volume parts (e.g., more than 100,000 units annually). Mid and low volume product runs or short life span product runs are often cost prohibitive.
Thus, there is a need for a new type of hydroforming system capable of handling large or thick walled workpieces, yet is relatively small, simple, and inexpensive in construction and operation. Such systems have been attempted, See generally, U.S. Pat. No. 5,927,120 to Marando. Marando claims a device that allows use of a smaller die set. The die set is placed in an inflatable bladder against the die set""s tool holder. The bladder is designed to minimize the effects of the smaller die""s deflections during the hydroforming process. Also, U.S. Pat. Nos. 3,092,898 and 3,187,533 to Cave et al. use pressure arms and cylinders to minimize press deflections and thus allow reduction in overall press size.
Unfortunately, the invention in Marando does not create a large variety of workpiece shapes. The press in Marando is still large and expensive. Further, mid to low production runs are still cost prohibitive. The Marando system would also not be practical for complex large or long shaped pieces. Similarly, the Cave et al. patent had limited application and was intended to limit expansion of sheets bonded together so as to expand un-bonded passageways. Again, design flexibility and control were limited.
Accordingly, the present invention provides an improved hydroforming system. The improved system can eliminate the need for a solid steel die (or mold) set operated by a conventional high tonnage hydraulic press. The present invention utilizes a fabricated or bar-stock die set integrated to a series of adjustably placed hydraulic cylinders to create a self-contained operating unit.
The system includes a die set, a plurality of hydraulic cylinders and system controllers.
The die set is made up of a mounted lower die half and an adjacent movable upper die half. The die halves in combination having an interior surface that defines a shape of a die cavity. The upper die half having a first set of reinforcement plates attached along an exterior surface of the upper die half and the lower die half having a second set of reinforcement plates attached along an exterior surface of the lower die half.
The die halves can be comprised of either a plurality of individual plates or a plurality of solid steel bar-stock pieces fastened together to form a die cavity. The individual plates or bar-stock pieces can be fastened together by conventional means, such as welding or bolting.
The plurality of hydraulic cylinders includes a plurality of activation hydraulic cylinders and a plurality of clamping hydraulic cylinders. Each activation hydraulic cylinder has a first clamping chamber, a first extension chamber, a first translation capable linear movement/linear transition mounted rod (first cylinder rod) having a first translation capable linear movement/linear transition mounted rod end (first cylinder rod end), and a first piston. Each clamping hydraulic cylinders has a second clamping chamber, a second extension chamber, a second translation capable linear movement/linear transition mounted rod (second cylinder rod) having a second translation capable linear movement/linear transition mounted rod end (second cylinder rod end), and a second piston.
The activation hydraulic cylinders and clamping hydraulic cylinders are arranged on the periphery of the die set to distribute reaction forces as equally as possible. The disclosed embodiments show the activation and clamping hydraulic cylinders in opposing and alternating layouts. The system requires at least two activation hydraulic cylinders to be present. In another embodiment, the system only uses activation hydraulic cylinders.
The system is controlled by a computer control system. The computer control system includes linear transducers encased in each activation hydraulic cylinder that transmit continuous linear position data to the computer control system. The computer control system interprets incoming data from all of the activation hydraulic cylinders and monitors and controls hydraulic fluid flow into and out of each of the activation and clamping hydraulic cylinders to insure uniform speed, position, and self-alignment of the first cylinder rod ends. This measurement and control insures the mounted lower die half and the movable upper die half remain parallel with each other.
The system can have a single power unit to create both the fluid pressure used to form the workpiece and the hydraulic pressure used to clamp the plurality of activation and clamping hydraulic cylinders. Alternatively, multiple power units can be used.
The system can also have a plurality of support pillars affixed to the lower die half. The support pillars can place the hydroforming system at a height convenient for a typical worker. The support pillars can be affixed to the lower die half at one end and affixed to the floor at the other end. The support pillars can also support the weight of the entire system and prevent the system from moving during operation.
Other objects of the present invention will become more apparent to persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying figures.